Our results validated multiple multiple sclerosis-specific protein biomarkers in CSF (e.g. CD27 and CXCL13).24-26 In our serum samples, the levels of these proteins could not differentiate multiple sclerosis samples from controls nor were they biomarkers for multiple sclerosis subgroups in line with previous findings.24 Neurofilament light chain (NFL) belongs to a class of proteins released when there is neuro-axonal damage and can be detected in both CSF and blood as a biomarker for multiple sclerosis.37-39 In the current study, we did not measure NFL. Here, CD27 is linked to multiple sclerosis.